1. Log in to the system.
2. From the main dashboard, go to the System Setup module.
3. Under the User Accounts section, click on Manage User Accounts.
4. Scroll down to view the list of all users registered in the system.
5. Locate the user account you wish to deactivate.
6. Select the user by clicking the checkbox next to their name. The checkboxes are located in the last column of the user list.
7. Scroll to the bottom of the page and locate the Bulk Action section.
8. From the available options, select Deactivate User Account.
9. Click GO to apply the action.

The selected user's account will then be deactivated.